The present invention relates to a silent chain for transmitting power. Such chains are used in automotive transmissions, transfer cases, engine timing systems, and the like. More specifically, the present invention relates to a silent chain in which the outer flanks of each link plate have protruding surfaces near the apertures. The result is an increase in material at points of high stress, which improves the durability of the silent chain as compared with conventional silent chains.
Silent chains are formed by an arrangement of link plates in lateral and longitudinal directions. The links are interlaced and joined by pins inserted into apertures in the link plates, forming a chain that is used in conjunction with a sprocket. A typical chain is composed of inner links, which contact the teeth of the sprocket to provide power transmission, and guide links, which do not provide power transmission. Guide links are employed to maintain the chain on the center of the sprocket. A row of link plates, arranged in the lateral direction, typically has a number of inner links combined with guide links in the center or at both edges of the row.
Conventional silent chains face design problems. In a conventional chain, tension acts to increase the distance between the apertures. As a result, cracks or breakage occur in the zone where the distance between the outside flank and the edge of the aperture is the smallest. In the past, there have been unsatisfactory attempts to solve this problem. Japanese Laid-Open Patent Application No. 4-312161 by Takeda and Kotera teaches a silent chain link plate with an outward protrusion on the flank of the tooth portion of the link plate. Thus, unlike the present invention, it does not improve the durability of the link plate in the vicinity of the aperture. In another design, the width of the entire outer flank of the link plate was increased. However, this resulted in a decrease in the distance between the teeth of adjacent link plates and thus necessitated a decrease in the width of the sprocket teeth. Such a decrease in width made the sprocket teeth highly vulnerable to fracture or breakage.
In yet another design, the width of the outer flank was widened near the aperture by forming the edge of the flank as a straight surface that ran at an exaggerated slant off the vertical. The problem with this design was that it relied to a large extent on weak frictional forces to hold the sprocket teeth and link plate teeth in contact during engagement. As a result, slippage of teeth could not be prevented.
FIG. 7 is a front elevational view of a conventional silent link plate. Link plate 100 has link body 110 in which a pair of pinholes 101, 102 are formed for insertion of the connecting pins. Link body 110 has a pair of teeth 103, 104 which mesh with a sprocket (not shown). Tooth 103 is composed of inside flank 105 and outside flank 106 and tooth 104 is composed of inside flank 105 and outside flank 107.
Tension acts on the entire chain when a silent chain, composed of multiple link plates 100, is in operation and, therefore, the compressive force from the connecting pin acts on pinholes 101, 102 of link plate 100 in the direction of stretching the distance C between pinhole centers (pitch).
As a result, cracks or breakage can occur in zone A (or A') where the distance between outside flank 106 (or 107) and the edge of pinhole 101 (or 102) is the smallest.
Therefore, the strength of the link plate at zone A, A' is increased by increasing the distance between the edge of the pinhole and the outside flank through placement of outside flanks 106, 107 (shown by a double-dotted line in FIG. 7) more to the outside of conventional outside flanks 106, 107 shown by the solid line. However, in such a case, although the strength of the link plate is increased, the thickness of the sprocket belt that meshes with outside flanks 106, 107 of link plate 100 decreases and, as a result, the strength of the sprocket teeth decreases
Tilting of outside flanks 106, 107 can be increased, as shown by the broken line in FIG. 7, for increasing of the link plate strength in zone A, A' and insuring the thickness of the sprocket teeth. However, in such a case, the chain tends to skip over the teeth during sprocket engagement.
The present invention is directed at solving the above-described problems. It improves the durability of the link plate without decreasing the strength of the sprocket teeth or causing the sprocket teeth to slip when engaging with the chain.